Diagnosis threat is a psychosocial factor that has been proposed to contribute to poor outcomes following mild traumatic brain injury (mTBI). This threat is thought to impair the cognitive test performance of individuals with mTBI because of negative injury stereotypes. University students (N=45, 62.2% female) with a history of mTBI were randomly allocated to a diagnosis threat (DT; n=15), reduced threat (DT-reduced; n=15), or neutral (n=15) group. The reduced threat condition invoked a positive stereotype (i.e., that people with mTBI can perform well on cognitive tests). All participants were given neutral instructions before they completed baseline tests of objective cognitive function across a number of domains, psychological symptoms, and PCS symptoms, including self-reported cognitive and emotional difficulties. Participants then received either neutral, DT, or DT-reduced instructions before repeating the tests. Results were analyzed using separate mixed model analysis of variances (ANOVAs); one for each dependent measure. The only significant result was for the 2 × 3 ANOVA on an objective test of attention/working memory, Digit Span (p<0.05), such that the DT-reduced group performed better than the other groups, which were not different from each other. Although not consistent with predictions or earlier DT studies, the absence of group differences on most tests fits with several recent DT findings. The results of this study suggest that it is timely to reconsider the role of DT as a unique contributor to poor mTBI outcome.